This exploratory/development project addresses the widely observed challenge of heterogeneity in the response of persons with autism spectrum disorders (ASD) and intellectual disability (ID) to behavior therapy. Fundamental in the design of such therapy is the assumption that basic behavioral processes such as reinforcement and extinction operate in a manner that is consistent with the general principles of the science from which the therapy derives. However, converging evidence from studies of both humans with a variety of neuropsychiatric disorders (e.g., ADHD) and animal models thereof suggest that there may be cases and circumstances under which that assumption may be questionable or at least may require a somewhat different interpretation than is customary. If the underlying assumptions do not hold true in all cases, then outcomes of therapy may show unsatisfactory variability. The proposed project is a multidisciplinary analytic effort with inputs from behavior analysis, psychobiology, and cognitive neuroscience. In studies under well-controlled conditions, we will use combined methodology from those disciplines to test two hypotheses with children with ASD and severe ID: (1) Results of tests of behavioral allocation in response to disparities in and changes to schedules of effective reinforcer deliveries will correlate positivel with performance on procedures that require discrimination learning, and (2) Results of certain psychobiological measures will differentiate children who do and do not show high responsiveness in behavioral allocation to schedule disparities/changes.